1. Technical Field
The present disclosure relates to a power amplifier.
2. Description of the Related Art
There is a power amplifier as a circuit that outputs signals of which amplitude has been amplified for emission of radio waves from an antenna, for instance.
As the power amplifier, as illustrated in FIG. 11, a circuit which is composed of an N-channel MOS transistor 801, an inductor 802, and a band-pass filter 803 and in which pulse waves are used as input signals is widely used. In this configuration, however, output of the power amplifier has a waveform similar to the input pulse and includes harmonics.
Apart from FIG. 11, there is a pulse-type power amplifier using an inverter that is composed of an N-channel MOS transistor 902 and a P-channel MOS transistor 901, as illustrated in FIG. 12. In this configuration as well, harmonics are generated in output.
In the past, a power amplifier that synthesizes output of a plurality of amplifiers each receive pulse waves in order to reduce odd harmonics has been proposed (see International Publication No. 2008/032782, for instance). A duty ratio and a phase of pulse wave that are received by an amplifier are set independently of duty ratios and phases of pulse waves received by other amplifiers.
FIG. 13 is a circuit diagram of the power amplifier disclosed in International Publication No. 2008/032782. FIG. 14 is a timing diagram illustrating signal waveforms in components of the power amplifier of FIG. 13. The power amplifier of FIG. 13 synthesizes output of an inverter composed of an N-channel MOS transistor 1001 and a P-channel MOS transistor 1002 and output of an inverter composed of an N-channel MOS transistor 1003 and a P-channel MOS transistor 1004. As illustrated in FIG. 14, a duty ratio and a phase of each of timing signals A10, B10, and C10 to the components are set independently of duty ratios and phases of other timing signals, and output waveform is formed in a waveform similar to a sine wave, so that the odd harmonics are reduced.